Dynamic Creation in Qt of QSlider with associated QLCDNumber

Question

I was wondering what's the best way to go about the following scenario?

I am dynamically creating QSliders that I wish to link to an associated QLCDNumber for display. The thing is I would like to have tenths available, so I would like to have a conversion between the QSLider and the QLCDNumber to divide by 10. At this point all I keep really is the QSlider, the QLCDNumbers I just create and forgot about. Is there an easy way of doing the conversion and connection without having to keep too much information?

Thanks in advance.

Answer 1

I'd try something along the following lines:

// create a new signal in your parent widget
signals:
  void updateLCDNumber(double);

// and a slot which performs the conversion
private slots:
  void performConversion(int value)
  {
   double convertedValue = value * 0.1;
   emit(updateLCDNumber(convertedValue));
  }

// then set the signals/slots up like this
connect(mySlider, SIGNAL(valueChanged(int)), this, SLOT(performConversion(int)));
connect(this, SIGNAL(updateLCDNumber(double)), myLCDNumber, SLOT(display(double)));

Afterwards you can completely "forget" about your LCD number, i.e. you don't need to keep a pointer or reference.

EDIT: A solution for several sliders:

class MySlider : public QSlider
{
 Q_OBJECT
public:
 MySlider(QWidget *parent=0) : QSlider(parent)
 {
   connect(this, SIGNAL(valueChanged(int)), this, SLOT(performConversion(int)));
 }

signals:
  void updateLCDNumber(double);

private slots:
   void performConversion(int value)
   {
     double convertedValue = value * 0.1;
     emit(updateLCDNumber(convertedValue));
   } 
};

Now create MySlider instances instead of QSlider ones and connect your QLCDNumbers:

connect(mySlider1, SIGNAL(updateLCDNumber(double)), myLCDNumber1, SLOT(display(double)));
connect(mySlider2, SIGNAL(updateLCDNumber(double)), myLCDNumber2, SLOT(display(double)));
...

This way you can also implement different conversion factors and the like, just modify the MySlider implementation.

I hope that helps.

Answer 2

This is basically what I ended up using; it seems to work (though it violates the whole object oriented philosophy).

signalMapper= new QSignalMapper(this);
QObject::connect(tmpSlider, SIGNAL(valueChanged(int)), signalMapper, SLOT(map()));
sliderMapper->setMapping(tmpSLider, tmpLCDNumber);
QObject::connect(signalMapper, SIGNAL(mapped(QWidget*)), this, SLOT(updateLCD(QWidget*)))

...

void MyClass::updateLCD(QWidget* lcdNum){
    ((QLCDNumber*)lcdNum)->display(((QSlider*)(signalMapper->mapping(lcdNum)))->value()*.1);
}